WATER EXCRETION IN POTASSIUM-DEFICIENT MAN*

Abstract

Serial studies of urine concentrating ability were performed in man during progressive potassium depletion. A temporal dissociation between the ability to concentrate urine during hydropenia and the capacity to reabsorb water during osmotic diuresis was found. UMAX was resistant to potassium depletion until about 200 mEq of potassium had been lost, progressively fell as the potassium deficit was doubled, and then reached a threshold hypertonic to plasma despite continuing potassium depletion. Free water reabsorption during mannitol diuresis fell abruptly with potassium restriction, and approached zero at a time when appreciable concentrating ability was retained. With more severe potassium deficiency, urine became hypotonic to plasma with solute loading. The capacity to dilute urine after water loading was retained. Some considerations of the mechanism whereby potassium deficiency may alter water conservation are discussed.